This invention relates to mold equipment utilized in glass making. More specifically, the invention relates to a cooling system for use in molds, plungers and even mold rings utilized in the press-forming of glass into articles. In addition, the invention relates to both method and apparatus for altering the temperature of the mold equipment, and hence the ability to remove heat from such equipment over a wide range of production speeds.
In the pressing of glass articles from molten or semi-molten glass, the rapid and controlled exchange of heat between the glass and the mold equipment is extremely important. It is particularly important that the temperature of the mold equipment be kept within a range that is most advantageous for the pressing process. Such temperature range is limited by operational constraints, in that the range should not exceed the temperature at which the glass begins to stick or adhere to the mold equipment, or should such range be less than the temperature at which optical defects or checks are produced in the product. The temperature range limitation materially restricts the range of production speeds which conventional mold equipment may operate, since the known cooling systems forming a part thereof are engineered for a particular predetermined production speed, and thus to be operable, such equipment had to be utilized within a limited operating speed range of about 2-3.
The problem of maintaining the mold equipment within a limited temperature range during various production speeds is aggravated by differential rates of heat removal from the mold equipment depending upon the geometry of the article being formed. In the pressing of glass, the rate of heat removal from the molten glass by the mold equipment depends to a large extent on the glass thickness and its geometric shape in localized regions. If the glass article to be produced has regions of both broad flat or slightly curved surfaces and also regions of relatively sharp corners, the rate of heat exchange between the glass and the mold equipment can differ significantly between such regions. Accordingly, the cooling systems of the prior art were designed specifically, not only for predetermined production speeds, but also for the differential heat removal necessary adjacent the various areas at such predetermined production speed. Thus, in such conventional mold equipment both the thermal and the mechanical considerations of the equipment had to be incorporated into the design. In other words, the mechanical and thermal considerations were by necessity coupled together, which further limited the versatility of such equipment.
Examples of the coupled cooling systems of the prior art are set forth in U.S. Pat. Nos. 3,202,498; 3,258,324; and 4,094,657. Both U.S. Pat No. 3,202,498 and U.S. Pat No. 4,094,657 are concerned with the problems encountered in uniformly removing heat during the pressing of glass articles having substantial variations in geometric shape and thickness. That is, specific cooling systems had to be designed for each plunger which included specifically positioned cooling jets and/or cooling grooves and insulated portions formed within the body of the plunger per se. Thus, both the mechanical and the thermal design considerations of such plungers were integrally coupled together. U.S. Pat. No. 3,258,324 patent also incorporated specially designed jets within a cooling system and thermal conductors and thermal barriers formed within a sealed hollow plunger body. In addition, a castable core metal was provided within the thermally determinate hollow plunger body, which could be varied to vary the thermal conductivity of such hollow body. Versatility, however, was materially limited in view of the fact that thermal insulators and conductors forming a part thereof predetermined the heat removal adjacent various areas, which could not be varied when production rates were changed.
In order to overcome the above-noted deficiencies in the pressing of glass items, the cooling system of the present invention has been developed, and accordingly, it is an object of the present invention to provide a method of an apparatus for cooling glass molding equipment which is independent of the mechanical considerations for forming the molding part. In addition, it is an object of the present invention to provide a cooling system which has the capability of accomodating a wide range of production speeds of up to about 1000% while utilizing the same molding equipment.